1. Field of the Invention
Embodiments relate to an apparatus for straightening filaments, in particular, plastic monofilaments, with a transport device for transporting the filaments and a heating device including a heating channel that forms a transport path for the filament.
Embodiments further relate to a method for producing straightened filaments, in particular, plastic monofilaments, in which a filament is continuously transported through a heating channel of a heating device by a transport device and the heating channel is heated during the continuous transport of the filament through the heating channel.
2. Discussion of Background Information
Straightened filaments, in particular plastic monofilaments, are used, e.g., as fixing wires in the production of spiral screens or coil screens. These screens are produced in a two-stage process. First, coils are wound from monofilaments and stored intermediately. The coils are then deposited so that their cross-sectional surfaces partially overlap in a separate process. Fixing wires are inserted into the region of overlap produced. These wires serve as a hinge and produce a connection between the coils. In this manner, the coils are assembled to form a screen.
Plastic monofilaments that are made of thermoplastic materials are particularly preferred as fixing wires. These are typically delivered and stored wound on spools. With this type of storage, however, the filaments adopt the curved shape of the spool, which shape is also partially preserved following the unwinding. The further processing of the filaments to form fixing wires is, however, hindered by this residual curvature. It must be eliminated according to the given process-related requirements. This procedure is referred to as the straightening of the filaments.
The approach according to the prior art provides for the filaments that are to be used as fixing wires to be guided through holes of a heated metallic heating block before the insertion operation into the coils. Heating blocks of this type are, however, thermally sluggish and only react to intended temperature changes very gradually. This results in a dilemma in the production of straightened filaments.
On the one hand, the filament comprises sections which differ in the amounts of heat absorbed. In the production of coil screens, it is necessary occasionally to cut to length the filament used as a fixing wire. Additionally, the screen joining process, and therefore also the insertion operation, proceed discontinuously. In this process, an idle state of the filament occurs in the heating block. The amounts of heat absorbed during the idle state of the filament in the heating block thus differ from the amounts of heat that the filament absorbs during the continuous insertion operation. On the other hand, an overheating of the sections heated in the idle state of the filament must be prevented. An overheating would lead to irreversible material damage.
The temperature of the heating block must therefore be chosen so that it is high enough for a sufficient heating to take place in the continuous pass-through of the filaments on the one hand. On the other hand, the temperature must be selected so that it is low enough so that no irreversible material damage occurs in the idle state of the filaments. The necessity of finding a compromise between these requirements leads to straightening results of the filaments of a merely limited quality.
The document DE 10 2007 052 594 B4 and its family member U.S. Patent Publication No. 2010/0287775 relate to a method and an apparatus for producing coil screens. The disclosures of these documents are expressly incorporated by reference herein it their entireties An automated production method for coil screens is disclosed. The coils are produced by a winding device arranged moveably above a working surface. Through a movement of a joining device on this working surface, they are then connected to one another by the insertion of a fixing wire.
In an automated joining operation, it is, unlike a manual joining process, necessary to work with straightened filaments of high quality. The process of straightening of the filaments is also time-critical. In the sequence of the production process, only a defined window of time is available within which the straightened fixing wire can be inserted. During the required cutting-to-length of the fixing wire, and outside of the window of time available for the insertion, there consequently results an idle state of the fixing wire in the heating block and the absorption of an increased amount of heat by the filament. The absorption of the increased amount of heat, however, leads to an irreversible damaging of the material.
Furthermore, an intermediate storage of a straightened filament that is to be used as fixing wire is not expedient. An intermediate storage of this type would require another diversion and thus a bending of the previously straightened filament. The quality of the straightening result would thus be reduced.